26
Fig 10 Equivalent circuit of each alarm output
9.2.2 Intrinsic safety
Each of the two alarm outputs is a separate
galvanically isolated solid state switch. The EC-
Type Examination Certificate specifies that under
fault conditions the voltage, current and power at
each alarm output will not exceed those specified
for
simple apparatus
in Clause 5.4 of
EN50020:1994. This allows each of the BA354D
alarm outputs to be connected to any intrinsically
safe circuit protected by a Zener barrier or galvanic
isolator providing that the output parameters of
each circuit do not exceed:
Uo
28V dc
Io
200mA
Po
0.85W
No system certificate has been issued for the
BA354D alarm outputs, as the system certificate
for the circuit to which the alarms are connected
remains valid.
The maximum equivalent capacitance and
inductance of each BA354D alarm output is:
C
= 40nF
L
= 20µH
To determine the maximum permissible cable
parameters, the equivalent alarm output
parameters must be subtracted from the maximum
cable capacitance and inductance specified by the
system certificate of the circuit connected to each
alarm.
Fig 11 Typical alarm application
9.2.3 Programming and adjustment
When a BA354D is supplied with alarms the main
programme menu is extended as shown in Fig 12.
The two alarm functions appear between the 'C--P'
and the 'SCALE-t' functions, and each alarm may
be programmed as a rate or a total alarm.
For simplicity Fig 12 only shows the programmable
functions on the rate option of alarm AL1. Alarm 2
and the total options are identical except that the
total alarms do not have hysteresis.
The following table summarises each of the alarm
programme functions and includes a cross
reference to more detailed information. Again
only the functions on alarm AL1 are listed.
